Recently, an ultra-wideband (UWB) communication system or an UWB radar have been sought and various technical solutions have been studied. For example, in the UWB communication system, a data transmission rate has been increased in accordance with a time width of a pulse (burst pulse), since a band width is enlarged in accordance with shortening of the time width of the burst pulse.
So as to realize data transmission of the UWB communication system, a burst oscillation circuit for generating a short pulse has been used as a signal source.
For example, in a wireless data transmission method using the short pulse as the signal source, a short pulse of which time width corresponds to data is generated and band-limited by a band-pass filter, and then a signal (burst pulse) corresponding to the data is output.
Further, in a wireless data transmission method using the burst oscillation circuit, the burst oscillation circuit is turned on/off control based on the burst control signal, and burst oscillation signals (burst pulse) are generated by operating a burst oscillation circuit in a predetermined time period.
As described above, the systems of using a short pulse as a signal source or of using a burst oscillation circuit have been used to perform the data transmission by the UWB communication.
Incidentally, in a wireless data transmission method using a burst oscillation circuit, so as to increase a transmission speed of data (data transmission rate), it is preferable to shorten a burst oscillation time (pulse width of the burst pulse). For example, in a pulse communication using frequencies of a 57 GHz to 66 GHz band allowed for a specified low-power radio station, an available bandwidth may be widened to at most 9 GHz band width.
In this case, since a pulse width of approximately 110 ps which is a reciprocal number of the bandwidth may be used as a pulse width, in a manner of transmitting data by on/off of the burst oscillation circuit (burst pulse), a 9 Gbps data transmission may be realized in accordance with the frequency band width occupied by the burst pulse.
However, in existing semiconductor devices, particularly, in highly versatile CMOS elements, it is difficult to shorten the time width of the burst pulse to 110 ps. Such a problem is not only included in the specified low-power radio stations of the 57 GHz to 66 GHz band, but, for example, UWB (mainly, for a user terminal) using a 3 GHz to 10 GHz band, and a mission-critical wireless communication using a 70 GHz to 80 GHz band and an 80 GHz to 90 GHz, and the like.
Specifically, in the above described wireless data transmission method, it is not possible to effectively use the bandwidth, and it is difficult to sufficiently secure the data transmission rate.
Conventionally, various techniques for a pulse generator applied to a UWB communication or UWB radar, or techniques for transmitting data by frequencies in correspondence with data have been proposed.
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-174087
Patent Document 2: Japanese Laid-open Patent Publication No. S62-028908
Non-Patent Document 1: Tuan-Anh Phan et al., “A 18-pJ/Pulse OOK CMOS Transmitter for Multiband UWB Impulse Radio,” IEEE Microwave and Wireless Components Letters, Vol. 17, No. 9, September 2007